The present invention is generally directed to processes for the preparation of cold pressure fixable toner compositions, and more specifically the present invention is directed to processes for obtaining single and/or two component cold pressure fixable toner compositions comprised of a core of carbon black, and a tough polymeric shell generated by an interfacial polymerization process, wherein the shell monomer is dissolved in the core prior to polymerization. Accordingly, in an embodiment of the present invention there are provided processes for formulating in an economical, and simple manner cold pressure fixable toner compositions by dispersing or dissolving the shell components in the core material selected for the toner, followed by hydrolysis, and subsequently an interfacial polymerization. The toners resulting are useful for permitting the development of images in electrostatographic imaging systems, inclusive of electrostatic imaging processes wherein pressure fixing, especially pressure fixing in the absence of heat is selected.
Cold pressure fixing processes are known. These processes have a number of advantages in comparison to heat fixing, primarily relating to the requirements for less energy since the toner compositions used can be fused at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fused under high pressure, which has a tendency to severely disrupt the toner fusing characteristics of the toner selected. This can result in images of low resolution, or no images whatsoever. Also, in some of the prior art processes substantial image smearing can result from the high pressures required. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions when used for development cause in some instances images with high gloss that are of low crease resistance. Furthermore, the images resulting exhibit an undesirable carbon paper effect, thus there is a total or partial image transfer from the image substrate to neighboring substrates caused by pressures arising from normal handling. In contrast, images developed with the cold pressure compositions prepared in accordance with the process of the present invention posses a low gloss appearance on plain paper, and further there is no carbon paper effect observed. Also, the toner compositions prepared in accordance with the process of the present invention have hard shells thus enabling images of excellent resolution with substantially no background deposits. Accordingly, with the process of the present invention inner polymerization methods permit the formation of aromatic polyurea shells, that is polymers wherein the main chains are comprised of aromatic groups. These polymers possess different characteristics, for example they are tougher and stronger than several prior art shells prepared by the interfacial polymerization of, for example, an aromatic or aliphatic oil soluble component with a water soluble aliphatic amine or alcohol. Furthermore, when shells are prepared from water soluble aromatics, such as phenol derivatives, it is often necessary to use solutions of a high pH value. This adversely affects the interfacial polymerization and the efficiency of added surfactants such as poly(vinylalcohol). When the efficiency of the surfactants is decreased, it is difficult to prepare toner particles with the appropriate diameter for use in imaging processes, and in addition agglomeration of the particles results.
With further reference to the prior art, there is disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, which shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. In the U.S. Pat. No. 4,307,169, it is indicated that when magnetite or carbon black is selected they must be treated in a separate process to prevent migration thereof to the oil phase.
Interfacial polymerization processes are described in British Patent Publication No. 1,371,179, the disclosure of which is totally incorporated herein by reference, which publication illustrates a method of microencapsulation based on in situ interfacial condensation polymerization. More specifically, this publication discloses a process which permits the encapsulation of organic pesticides by the hydrolysis of polymethylene polyphenylisocyanate, or toluene diisocyanate monomers. There is no teaching, however, in the '179 publication relating to a process for preparing cold pressure fixable two component toners. Also, the wall forming reaction disclosed in the aforementioned publication is initiated by heating the mixture to an elevated temperature at which point the isocyante monomers are hydrolized at the interface to form amines, which in turn react with unhydrolized isocyanate monomers to enable the formulation of a polyurea microcapsule wall. One difficulty associated with the process of the '179 publication resides in the possibility of the continued reaction of monomer after packaging. Therefore, unless the monomer selected is reacted during the preparation, there will be continued hydrolysis with evolution of carbon dioxide resulting in the formation of pressure. This problem, which is overcome with the process of the present invention, is also illustrated in European Patent Application No. 84870186.8. Furthermore, with the process of the present invention the appropriate solvent selection (the amount of, for example, isocyanate shell materials used), the improved control of the hydrolysis reactions being accomplished as determined by an analysis of the kinetics thereof, and the design of a suitable reaction temperature profile enable the formation of toners with acceptable levels of residual isocyanates, that is no monomers are detectable by thermogravimetric analysis at the highest sensitivity setting. The process of the present invention also permits the controlled formation of oligomers which impart improved fusing characteristics to the resulting toner compositions. Additionally, with the process of the present invention the disadvantages of the post-treatment of the toner compositions prepared under controlled conditions are prevented thereby avoiding continued evolution of carbon dioxide, and excessive aggregations.
Furthermore, there is disclosed in U.S. Pat. No. 4,552,811, a process for capsule formation by an an inner polymerization process. In this process, the reactants forming the interfacial materials are dispersed in the water phase, and not in an organic phase.
Moreover, there is disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, interfacial polymerization processes for pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component.
Additionally, illustrated in a copending application U.S. Ser. No. 621,307, entitled Single Component Cold Pressure Fixable Encapsulated Toner Composition, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676, the disclosure of which is totally incorporated herein by reference, directed to single component magnetic cold pressure fixable toner compositions. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process. More specifically, there is illustrated in the aforementioned copending application cold pressure fixable magnetic single component developers with small amounts of carbon black and large amounts of magnetite.
Furthermore, other prior art that might be of background interest includes U.S. Pat. Nos. 4,254,201; 4,465,755; 4,520,091; and Japanese Patent Publication No. 58-100857. The Japanese publication discloses a capsule toner with high mechanical strength, which is comprised of a core material including a display recording material, a binder, and an outer shell enclosing the core material, which outer shell is preferably comprised of a polyurea resin. In the U.S. Pat. No. 4,520,091, there is disclosed encapsulated electrostatographic toners wherein the shell material comprises at least one resin selected from polyurethane resins, a polyurea resin, or a polyamide resin. In addition, the U.S. Pat. No. 4,465,755 discloses a pressure fixable toner comprising encapsulated particles containing a curing agent, and wherein the shell is comprised of a polyurethane, a polyurea, or a polythiourethane. Moreover, in the U.S. Pat. No. 4,254,201 there is illustrated pressure sensitive adhesive toners comprised of clustered encapsulated porous particles, which toners are prepared by spray drying an aqueous dispersion of the granules containing an encapsulated material.
Accordingly, there is a need for improved processes that will enable cold pressure fixable toner compositions with hard shells. Also, there is a need for improved processes that will permit the formulation of cold pressure fixable toner compositions with carbon black, or magnetite as the core material. There is also a need for improved processes that will enable cold pressure fixable toner compositions with mixtures of carbon black and magnetite as the core material. Additionally, there is a need for simple economical interfacial polymerization processes that will allow hard shells to be generated for cold pressure fixable toner compositions. There is also a need for improved processes that will provide cold pressure fixable toner compositions with hard shells, and wherein the monomer selected for the shell is dissolved in the core. Moreover, there is a need for a process that permits the selected control of the toner electrical properties, inclusive of dielectric constant characteristics, and triboelectrics charging properties. The aforementioned properties, and characteristics properties are dependent primarily on the type of carbon black dispersion, and the carbon black loading.
Another advantage associated with the process of the present invention resides in the ability to control the shell properties thereby permitting, for example, desirable toner properties inclusive of appropriate toner particle size, and acceptable fixing and smear properties. Indirectly, there is also permitted in accordance with the process of the present invention the monitoring of small changes in core properties, such as the viscosity thereof, and the pigment dispersion characteristics. The aforementioned advantages are demonstrated hereinafter, and in particular in Example X.